Sudomy VS Sublist3r

That said, keep in mind that not everything is going to find its way indexed in Google. If it's subdomains you're after, you can use tools like Sublist3r or Sudomy to pull data from multiple sources (not just DNS).

You cannot hide anything on the internet anymore, the full IPv4 range is scanned regularly by multiple entities. If you open a port on a public IP it will get found.

If it's a obscure non-standard port it might take longer, but if it's on any of the standard ports it will get probed very quickly and included tools like shodan.io

The reason why I'm repeating this, is that not everyone knows this. People still (albeit less) put up elastic and mongodb instances with no authentication on public IP's.

The second thing which isn't well known is the Certificate Transparency logs. This is the reason why you can't (without a wildcard cert) hide any HTTPS service. When you ask Let's Encrypt (or any CA actually) to generate veryobscure.domain.tld they will send that to the Certificate Transparency logs. You can find every certificate which was minted for a domain on a tool like https://crt.sh

There are many tools like subdomain.center, https://hackertarget.com/find-dns-host-records/ comes to mind. The most impressive one I've seen, which found more much more than expected, is Detectify (which is a paid service, no affiliation), they seem to combine the passive data collection (like subdomain.center) with active brute to find even more subdomains.

But you can probably get 95% there by using CT and a brute-force tool like https://github.com/aboul3la/Sublist3r

Sublist3r

sublist3r = https://github.com/aboul3la/Sublist3r

Try following this step too - click here

For those asking what tool I was using, its called sublist3r (https://github.com/aboul3la/Sublist3r). It uses open source intelligence gathering (public info) as well as brute force to try and enumerate subdomains.

That said, keep in mind that not everything is going to find its way indexed in Google. If it's subdomains you're after, you can use tools like Sublist3r or Sudomy to pull data from multiple sources (not just DNS).

In a real-world scenario. You're likely to come across a target with more than one domain, each having it's own subdomains. There's plenty of tools that you can use to discover these. Again, PyRCON offers some options for this but I like tools such as sublist3r and publicly available records such as security trials.

Kali has sublist3r

The downside is, wildcard DNS fills the results with false positives because every subdomain will return an IP address. There was an issue raised for sublister a few years ago (still open) that raised this exact issue: https://github.com/aboul3la/Sublist3r/issues/118